This invention relates to a superconducting magnet for MRI suitable for generating a homogeneous field, and to an MRI diagnostic apparatus.
A typical superconducting magnet for MRI of the prior art is described in U.S. Pat. No. 4,876,510 entitled "Apparatus for Nuclear Spin Tomography Having Superconducting Base Field Coils and a Radiation Shield". This reference discloses a coil arrangement in which six small superconducting coils having a substantially equal mean winding radius are disposed symmetrically with respect to a central plane of a magnet and coaxially along a central axis of this magnet.
When the position and magneto-motive force of each of the small superconducting coils are regulated in the coil arrangement described above, an excellent homogeneous field devoid of second to tenth order inhomogeneous fields can be generated in a substantially spherical region at the center of the magnet. To obtain a tomogram having higher quality in the field of nuclear magnetic imaging, however, a more homogeneous field is required.